The proposed deal to sell KBWB Channel 20 in San Francisco and a UHF station in Detroit to a group headed by former KTVU Channel 2 general manager Kevin O’Brien (pictured) has fallen through. The seller, Granite Broadcasting, announced today that it is backing out of the $150 million deal and putting the stations back on the market. According to Broadcasting & Cable magazine, Granite had been trying to sell the two stations to pay off debt, but got a new line of credit earlier this month. Now that things aren’t so desperate, Granite decided to back out of the deal. The Detroit station’s value is increasing because it has landed a new network, but the SF station is losing its WB affiliation and is in a tougher situtation. O’Brien’s group, which includes four private equity firms, can still make a bid on the SF station.